I have three issues Please HELP!

1. I want to create a list validation in a cell on sheet1. When the drop
down is selected it will show a list based on data in cloumn A on SHEET2.
When the item is selected it will actually populate the cell with the
corresponidng data in the same row but from column B. If I select corn below
in the list validation in will pop the cell with yellow?

IE: Sheet 2 column a cloumnb
Corn Yellow

2. In this same list validation cell. I want to prevent a user from typing
anything but selecting from a list. On other list validation cells excel will
still allow me to tpye something off the wall in the list validation cell?

3. I have 5 combobox. When one is selected it filters the data in the
worksheet. How can I have it to shade the box as selected. Then when I click
on another box it unshades the previous and shades the one clicked?